This research is aimed at identifying interacting loci that contribute to reproductive isolation between the model plant Physcomitrella patens and its wild relative Physcomitrium pyriforme. A combination of classical genetic and modern genomic approaches will be used to identify genes that fail to interact properly in a hybrid genetic background. Such maladaptive interactions among functional loci may contribute to a wide variety of complex diseases in humans. The P. patens model provides a simple genetic system where the molecular genetics of multilocus interactions can be easily manipulated and studied. The identification of molecular variants underlying complex traits, like reproductive isolation, opens several new avenues of research into the specific mechanisms of adaptation and speciation. [unreadable] [unreadable]